Second External Display Flickering

I noticed out of the corner of my eye that during the evening, when f.lux has transitioned to overnight warm hues, my second but not my first external monitor flickers every 5-10 seconds.

This secondary monitor never flickers when during the day. I can even disable f.lux at night and the annoying flickering stops!

Has anyone else experienced this problem?

I am using Windows 7 with a NVIDIA Quadro 1000M graphics controller on a Lenovo ThinkPad W520 notebook with the Lenovo dual DVI port docking station. It's worked perfectly fine until recently - or at least I just started noticing it.